Abstract
The rice bugs Leptocorisa chinensis Dallas, Lagynotomus elongatus (Dallas), Cletus punctiger (Dallas) and Stenotus rubrovittatus (Matsumura) are serious economic pests of rice crops in Japan. To clarify the ripening stages of spikelets preferentially attacked by these bugs in paddy fields, rice bugs were individually released for three days onto a rice panicle at stages of maturation 7, 14, 21 and 28 days after heading (DAH). The spikelets were classified into three groups according to position in a panicle, which is closely related to the flowering order. Group A contained top spikelets of the primary and secondary branches and bottom spikelets of the primary branches (early flowering). Group B contained spikelets of the primary branches except the top, second and bottom spikelets (mid flowering). Group C contained the other spikelets (late flowering). The bugs chose to feed on the spikelets in Group A and Group B on 7 DAH. At 14 and 21 DAH, however, bugs preferred the spikelets in Group C to those in the other two groups. In L. chinensis, L. elongatus and S. rubrovittatus, the total number of damaged spikelets decreased with maturation of the panicle, whereas there was no remarkable change in the number of spikelets damaged by C. punctiger. These results suggest that all species of rice bugs except C. punctiger selectively damage spikelets of ovaries are developing with lengthwise to sidewise elongation, whereas C. punctiger mainly attacks spikelets of ovaries developing with lengthwise to thickness elongation.
